Determines if the caller should do one of several things:
- seek/skip to the next row (MatchCode.SEEK_NEXT_ROW)
- seek/skip to the next column (MatchCode.SEEK_NEXT_COL)
- include the current KeyValue (MatchCode.INCLUDE)
- ignore the current KeyValue (MatchCode.SKIP)
- got to the next row (MatchCode.DONE)